-LRB- CNN -RRB- -- The discovery of horse DNA in hamburgers on sale at supermarkets in Ireland and Britain is testing the appetite of meat lovers there .

The Food Safety Authority of Ireland said Tuesday that 10 out of 27 hamburger products it analyzed in a study were found to contain horse DNA , and 23 of them tested positive for pig DNA .

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The horse-tainted burgers , on sale at several different supermarket chains , came from two meat processing plants in Ireland and one in Britain , the Irish authority said .

`` This raises concerns in relation to the traceability of meat ingredients and products entering the food chain , '' it said , but noted that the findings posed no risk to public health .

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In nine out of the 10 burger samples , the horse DNA was found at very low levels , the authority said , but in one sample from Tesco , Britain 's largest retailer , the horsemeat accounted for about 29 % of the burger .

Tesco responded by pulling from its shelves all products from the company that had supplied the dubious burgers .

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`` We understand that many of our customers will be concerned by this news , and we apologize sincerely for any distress , '' Tesco said .

The retailer is working with Irish and British authorities and the supplier to work out what had happened , it said .

Alan Reilly , the chief executive of the Irish food authority , said there was a `` plausible explanation '' for the pig meat finding its way into the burgers , since meat from different animals is processed at the same plants . But he said there was `` no clear explanation at this time '' for the presence of the horsemeat .

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`` In Ireland , it is not in our culture to eat horsemeat and therefore , we do not expect to find it in a burger , '' Reilly said . `` Likewise , for some religious groups or people who abstain from eating pig meat , the presence of traces of pig DNA is unacceptable . ''

Many British and Irish people expressed their distaste over the revelations on social media .

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Some Twitter users said they were n't surprised to hear about the questionable origins of the burgers , while others debated the ethics of eating horsemeat .

And then there were those who saw an opportunity for attempts at humor .

`` Going to #tesco and expecting a beef burger . Instead you get #horsemeat . Sounds to me like foal-play , '' wrote Twitter user Matt Oswin under the username @BrushmanLestar .

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Irish Food Safety Authority finds horse DNA in 10 out of 27 burgers it tested

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The hamburgers are on sale in supermarkets in Ireland and Britain

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The agency finds 29 % of a burger from Tesco to be made of horsemeat

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Tesco says it has withdrawn from sale all products from the supplier in question